The invention relates generally to wireless communication systems, and more particularly to packet detection in wireless communication systems using time frequency codes.
Digital wireless communication systems are widespread, and there are numerous methods that may be used in wirelessly transmitting information. In many such methods information is transmitted in discrete packets. The use of discrete packets for data transfer provides a number of benefits, often including for example increased bandwidth utilization in the presence of multiple devices and standardization of overhead communication.
The discrete packets generally include a header for various overhead information and a payload for data. The overhead may include information regarding the transmitter and the intended receiver, information regarding the length of the payload, and various other types of information relating to the transmission of information. For example, in some systems a packet includes a preamble and a payload, and the preamble includes a predefined preamble sequence, a prefix, a guard interval, and possibly channel estimation symbols. The preamble sequence is a known sequence useful for detecting the presence of a packet, and the known sequence may also include sufficient information for a receiver to be able to frame the packet as well.
At times wireless communication systems may be operating in noisy environments or other environments which adversely affect received signals. In many such environments payload information may be correctly decoded through the use of appropriate error correcting coding and interleaving of data. Moreover, once a preamble is detected other functions, such as automatic gain control processing, frequency offset estimation, and channel estimation, may be performed to improve processing of received signals. Detection of the known sequence in the overhead information may be problematic, however, particularly when the environment includes multiple transmitters whose signals mutually interfere with one another.
As an example, some wireless communication systems may use multiple frequency sub-bands for transmission of information. Having any particular transmitter vary the use of frequency sub-bands over time may increase total potential communication bandwidth while also minimizing interference issues with respect to any one particular sub-band. The sequence by which the transmitter varies use of frequency sub-bands may be referred to as a time frequency code (TFC), with each TFC defining a logical communication channel. In some proposed systems the logical communication channels are not necessarily orthogonal to one another in time, space, or frequency usage. Thus, different transmitters may be transmitting at the same frequency sub-band at the same time, mutually interfering with each other's signal and increasing the difficulty of detecting preamble sequences.